1. Field of the Invention
The present invention relates to a construction machine such as an excavator provided with a cab allowing an operator to enter therein.
2. Description of the Background Art
The background art of the present invention is described by an example of an excavator shown in FIGS. 6 through 8.
The excavator shown in FIGS. 6 through 8 is provided with a crawler-type lower propelling body 1, and an upper slewing body 2 loaded on the lower propelling body 1 to be slewable about an axis vertical to the ground. The upper slewing body 2 includes: an upper frame 3; a cab 4 serving as an operation room in which an operator is allowed to enter and disposed on a left portion or a right portion (generally, on the left portion) of the upper frame 3; a working attachment 6 having a boom 5 and the like and disposed on a lateral side (generally on a right side) of the cab 4 to be raised and lowered; and a counterweight 7 provided at a rear end of the upper frame 3.
A front left portion of the upper frame 3 constitutes a cab attachment portion 8 as shown in FIGS. 7 and 8. The cab 4 is loaded on the cab attachment portion 8 via a plurality of cab mounts 9. The cab mounts 9 are disposed at four corners on a bottom portion of the cab 4, in other words, disposed respectively at both ends in a lateral direction (left and right directions) of the construction machine on each of a front portion and a rear portion of the bottom portion in a longitudinal direction (front and rear directions) of the construction machine.
As disclosed in the specification and drawings of Japanese Unexamined Patent Publication No. 2004-189089 and Japanese Patent No. 3671790, each of the cab mounts 9 is formed as an anti-vibration mount which has an elastic member (normally made of an anti-vibration rubber material) and elastically supports the cab 4 so as to allow the cab 4 to be vertically and horizontally displaced relatively to the upper frame 3 within a predetermined range by the elastic deformation of the elastic member, thus damping vibrations of the cab 4 during driving. Besides, each of the cab mounts 9 exerts a resistive force, against a load acting on the cab 4 in such a direction as to remove the cab 4 from the cab attachment portion 8 of the upper frame 3 when the machine rolls over, by an elastic expansion of the elastic member of the cab mount 9.
Japanese Unexamined Patent Publication No. 2006-348509 discloses a machine which includes, in addition to conventional cab mounts to be disposed at four corners on a bottom portion of a cab, other damping mechanisms to be disposed at respective positions away inwardly of the cab from the rear-side right and left pair of cab mounts. These other damping mechanisms are additionally provided to enhance supportability of a rear portion of the cab, in view of a point that the front portion of the cab is provided with relatively a few reinforcing members which are light, in order to secure a front view, while the front portion of the cab is provided with relatively many reinforcing members which are heavy.
The excavator shown in FIGS. 6 through 8 has a drawback of requiring upsizing each of the cab mounts 9 to prevent the cab 4 from disengaging from the cab attachment portion 8 when the machine rolls over. Specifically, in the case where the excavator rolls over on the side of the cab 4, that is, on such one side of the right and left sides that the cab 4 is placed down (generally toward the left side), initially the cab 4 touches down the ground and then the excavator further rolls over about an outer-side upper end of the cab 4 as a support on the ground so that the lower propelling body 1 takes off the ground: at this stage, the outer-side upper end of the cab 4 receives an upward reaction force from the ground, which force acts on the cab 4 as a moment which rotates the cab 4 in such a direction as to remove a laterally outer end of the cab 4 from the upper frame 3, about a contact portion (generally, longitudinally extending axis) between a laterally inner-side lower end of the cab 4 and a vertical plate 3a shown in FIG. 7 (the vertical plate 3a is a plate member standing upright on the upper frame 3 for supporting the boom 5) as a support. In this occasion, a tensile load initially acts on the left-side cab mounts 9, 9 located on the laterally outer-side of the cab, and, only after the fracture of the left-side cab mounts 9, 9, the right-side cab mounts 9, 9 can receive the load. Hence, to prevent the cab 4 from removal from the upper frame 3a, there is demanded high support strength especially for the left portion of the cab 4. However, the arrangement as shown in FIGS. 6 through 8, in which the cab mounts 9 are equally disposed at the four corners on the bottom portion of the cab 4 respectively, cannot meet the aforementioned demand, and the cab 4 is hardly prevented from the removal without upsizing each of the cab mounts 9.
Japanese Unexamined Patent Publication No. 2006-348509 discloses an excavator additionally provided with other damping mechanisms at a rear portion of a cab; however, even in this type of excavator, the cab is hard to efficiently prevent from its removal. Since the disclosed additional damping mechanisms are provided at respective positions largely away from the rear-side left and right pair of cab mounts toward a laterally middle position to enhance weight supportability of the cab for the great weight of the rear portion of the cab, an outermost cab mount of the cab mounts is broken first, when the excavator rolls over, and only thereafter, the additionally provided damping mechanism disposed at the inner side of the broken cab mount receives the load. In other words, the cab mounts and the additionally provided damping mechanisms successively and individually receive the load, which hinders enhancing the strength for preventing the cab from removal, regardless of the addition of the damping mechanisms. In short, this technology is only capable of extending a time until the removal of the cab, not providing a fundamental solution.
There may be proposed another measure of adding a grapple other than the cab mounts to the upper frame side for preventing removal of a cab when the machine rolls over; however, this is not advantageous because of involving an intolerable increase in the number of assembling steps, cost, and required space for installation.